Ability to exclude a device(s)/device groups from a Dashboard widget?

To add on to what Stuart said, most widgets allow you to filter what they show you in a number of ways. Probably the most efficient way to do this is by using dashboard tokens to allow for widespread filtering by group. 

First you’ll want to group these file servers into a group or a set of subgroups of a group. If they aren’t already grouped in a way that works for this, it’s possible to have more than one group hierarchy at work at a given time for given sets of devices; you can create a group for just this purpose.  (so you won’t need to disrupt your existing grouping/organization) https://www.logicmonitor.com/support/devices/device-groups/device-groups-overview
Then, you’ll want to leverage dashboard tokens to reference this group in the filters for any widgets that support them. Here’s an article that covers it: https://www.logicmonitor.com/blog/streamline-workflows-with-dashboard-tokens
Finally, as Stuart explained, because you want to exclude the set of devices that are file servers, you will use a glob expression to do that. There’s a detailed document here https://www.logicmonitor.com/support/terminology-syntax/glob-expressions, with a bunch of examples. I think the glob for an expression which excludes a group called “File Servers” and any subgroups would look like this “!(File\sServers*)” Once you do it, you should be able to see it in the dashboard widgets immediately. 
You could, of course, hard code things, but this is nice because it’s easy to replicate and change. 

Depends on the widget, but if the field supports glob expressions, you can negate by using the ! bang symbol.

You can know it’s working based on what shows up in the dropdown as you type the filter. 

For example, if you wanted to exclude all devices with XYZ in the name, you’d do a filter like this:

(!(*XYZ*))

I’ll add this one as well: Dynamic Dashboards | Community (logicmonitor.com)

We use that resource selector widget everywhere, make a dashboard… add that widget, set it aside as your main template to clone every time you make a new dashboard.